Timed Refinement for Verification of Real-Time Object Code Programs
Dubasi, Mohana Asha Latha
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Real-time systems such as medical devices, surgical robots, and microprocessors are safety-critical applications that have hard timing constraint. The correctness of real-time systems is important as the failure may result in severe consequences such as loss of money, time and human life. These real-time systems have software to control their behavior. Typically, this software has source code which is converted to object code and then executed in safety-critical embedded devices. Therefore, it is important to ensure that both source code and object code are error-free. When dealing with safety-critical systems, formal verification techniques have laid the foundation for ensuring software correctness. Refinement based technique in formal verification can be used for the verification of real-time interrupt-driven object code. This dissertation presents an automated tool that verifies the functional and timing correctness of real-time interrupt-driven object code programs. The tool has been developed in three stages. In the first stage, a novel timed refinement procedure that checks for timing properties has been developed and applied on six case studies. The required model and an abstraction technique were generated manually. The results indicate that the proposed abstraction technique reduces the size of the implementation model by at least four orders of magnitude. In the second stage, the proposed abstraction technique has been automated. This technique has been applied to thirty different case studies. The results indicate that the automated abstraction technique can easily reduce the model size, which would in turn significantly reduce the verification time. In the final stage, two new automated algorithms are proposed which would check the functional properties through safety and liveness. These algorithms were applied to the same thirty case studies. The results indicate that the functional verification can be performed in less than a second for the reduced model. The benefits of automating the verification process for real-time interrupt-driven object code include: 1) the overall size of the implementation model has reduced significantly; 2) the verification is within a reasonable time; 3) can be applied multiple times in the system development process.